Coatings typically require acceptable level of clarity, for example in the case of clearcoat applications, hardness, impact resistance, environmental etch resistance, weatherbility, scratch and mar resistance, and adhesion to basecoats and/or other substrates.
Scratch and mar resistance and/or recovery are significantly important in coating markets for wood, plastic, and metal substrates. Such recovery or resistance to damage of surfaces is useful in preserving the aesthetics of surfaces in a number of finishes in applications, such as, automotive interior and exteriors, exterior of rail cars, consumer electronic goods, displays, sporting goods, leather goods, wood furniture, wood flooring, metal appliances, etc. Additionally, such a feature is useful for protecting surfaces when they are damaged from corrosion, e.g. protection of surfaces in light and medium duty equipments such as tractors, farm equipments, pipes, tanks in the oil, gas and chemical industries.
However, simultaneously satisfying environmental etch resistance and hardness with scratch and mar resistance has been a challenge for coating applications. For example, increasing cross-link density may result in increasing hardness and slows diffusion of small molecules through the coating. Thus, this may provide increased barrier to environmental agents like acid or solvents leading to improved environmental etch resistance of the coating. However, the coating may become brittle, and easily broken with scratching and marring of the surfaces; therefore, leading to unsightly damage. Solving this dichotomy has been a challenge for the industry.
Accordingly, there is still in need for a polyurethane coating composition with adequate hardness and scratch and mar resistance as well as self-healing properties.